1. Field of the Invention
The present invention relates to a heterodyne-type for measuring the frequency characteristics, such as attenuation, amplification and phase, of quadripoles.
2. Description of the Prior Art
Heterodyne spectrum or network analyzers of the type generally set forth above for measuring the frequency characteristics of quadripoles, for example for measuring the quadripole transfer function (attenuation, amplification or phase) are known in the art from the German published application 24 52 744. The frequency of the locked oscillator thereof correspond exactly to the intermediate frequency to which an unknown signal in an indicator branch is converted. It is also known in the art to provide this oscillator as a frequency-variable oscillator within very narrow limits of a few kilohertz, which is determined by the accuracy of the oscillator, so that in the case of a very narrow intermediate frequency bandwidth, the unknown signal may be set precisely at the middle of the band.
With such a known analyzer, it is not possible to measure-frequency-converting quadripoles in which the input and output frequencies are different.